Depending on if you have the Mach Stereo, or the premium. Speakers are 5x7/6x8 size for rear doors. You can do the same for front, although the Mach Stereo uses a 5 1/4 separates setup in front door. Crutchfield or any decent auto stereo shop can sell you the wire adapters so your not chopping and crimping new connectors. As far as amps, theirs a small subwoofer one in the passenger side woofer housing. The factory subwoofer is 8 inch size. If you want a heavier bass, and can do without the 3rd seat, a bigger box with dual 10 or 12 inch speakers and a bigger sub amp will definitely improve your bass. Again if Mach, you have a small 4 channel amp below head unit. You will need adapters for both amp plugs to run aftermarket amps. Do your homework matching speaker sensitivity to amp output. Especially important if you don't have a front amp, and your depending on the basic 15 watt x4 built in amp. Hope that helps.
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